
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21767.8    171.3805    22529.21    21431.88    22103.72
experime |  17,281    21880.44     174.857    22986.22     21537.7    22223.18
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -112.6405    244.8393               -592.5335    367.2524
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.4601
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3227         Pr(|T| > |t|) = 0.6455          Pr(T > t) = 0.6773
